RFR: 8328181: C2: assert(MaxVectorSize >= 32) failed: vector length should be >= 32

[Jatin Bhateja]

This bug fix patch tightens the predication check for small constant length clear array pattern and relaxes associated feature checks. Modified few comments for clarity.

Kindly review and approve.

Best Regards,
Jatin

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Commit messages:
 - Adding Testpoint
 - Some comments modifications
 - 8328181: C2: assert(MaxVectorSize >= 32) failed: vector length should be >= 32

Changes: https://git.openjdk.org/jdk/pull/18464/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18464&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328181
  Stats: 21 lines in 5 files changed: 6 ins; 0 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/18464.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18464/head:pull/18464

PR: https://git.openjdk.org/jdk/pull/18464